Heat exchanger



March 18, 1952 P. c. KEITH HEAT EXCHANGER 4 Sheets-Sheet 1 Filed June12, 1946 .1 Rw Y ova m m] R E C v T N T l March 18, 1952 P. c. KEITHHEAT EXCHANGER 4 Sheets-Sheet 2 Filed June 12, 1946 BY LC HTTORNEY March18, 1952 P. c. KEITH HEAT EXCHANGER 4 Sheets-Sheet 3 Filed June 12, 1946INVENTOR fira'ua/ f. fizz/ BY [I ATTORNEY Patented Mar. 18, 1952 HEATEXCHAN GER Percival 0. Keith, Peapack, N. J assignor to Hy-- drocarbonResearch, Inc., New York, N. Y., acorporation of New Jersey ApplicationJune 12, 1946, Serial No. 676,142

9 Claims. (Cl. 257228) The present invention relates to an improvedexchanger for recovering the cold content of the outgoing oxygen andnitrogen products of rectification, which may be at a temperature ofabout 280 F., in the production of oxygen by the liquefaction andrectification of air.

Cold accumulators or regenerators (hereinafter referred to as coldexchangers) of large cold-absorbing capacity are well known. In thesecold exchangers, the relatively warm incoming air and the relativelycold outgoing oxygen and nitrogen products of rectification arealternately passed with periodically reversed operation, so that streamsof warm air are flowed through the same packing-filled spaces as thecold oxygen and nitrogen traversed during the preceding step in theprocess, the hi h-boiling impurities deposited in these spaces duringthe passage of the air therethrough being removed by sublimation duringthe subsequent flow therethrough of the products of rectification.

An improved form of cold exchanger is described, for example, incopending application Serial No. 641,276, filed January 15, 1946, nowPatent No. 2,529,516. The exchanger of said application comprises acylindrical shell, in which are disposed a large number of tubes dividedinto two sets. Each tube of both sets has an interior accordion fin offoil-like metal of high heat conductivity disposed to form channelsextending longitudinally through the tube and an accordion fin on theexterior thereof also arranged to form longitudinal channels. Oxygenflows through one set of tubes, constituting a minor portion of thetubes, which set of tubes is substantially uniformly distributed throughthe other set of tubes. Air and nitrogen alternately flow through theinterior of the other set of tubes and through the longitudinal channelsformed by the fins on the exterior of all of the tubes, the flow ofthese two media being periodically reversed, so that during one cycle ofoperation, the air flows through the channels in the interior of thesetubes of the second set and the nitrogen through the channels on theexterior of all of the tubes, and during a succeeding cycle of operationthe nitrogen flows through the channels in the interior of these tubesof the second set and the air fiows through the channels on the exteriorof all of the tubes.

While the construction of said patent application represents amarkedadvance over prior known exchangers, it does involve certainobjections; for example, for eflicient cold transfer, it is necessary tobondthe exterior fins of one tube to the exteriorfins of contiguoustubes, or at least have them in metal-to-metal contact. Another featureof this exchanger which is somewhat objectionable is that the oxygentubes must be provided with expansion joints to compensate fordifferential expansion and contraction taking place between these tubes,which generally are of copper, and the portion of the shell, generallyof nickel steel, between the two header plates at each end of the shellthrough which the oxygen tubes pass and to which they are fastened.Further, it is important to note that in this prior construction, sincethe set of oxygen tubes is distributed through the other set of tubesand the air stream is to take up the cold content of both the oxygen andnitrogen streams, the pretesting of the individual tubes can onlyindicate the heat transfer efliciency between air and one product ofrectification and not between air and both products of rectification asis desired. Hence, in order to determine whether satisfactory coldexchange will take place in the operation of the exchanger, it isnecessary to fabricate and assemble a complete exchanger and then testit by flowing the oxygen and nitrogen products of rectification and airand ascertaining the temperature of the exiting gas streams; it is notpossible from a test of an individual tube having the fins on both theinterior and exterior thereof to determine whether, when a plurality ofsuch tubes are assembled, satisfactory cold exchange will take place,such that the air will be cooled to the desired low temperature by boththe oxygen and nitrogen products of rectification.

Among the objects of this invention is to provide a cold exchanger soconstructed and designed that each individual unit can be tested andevaluated to determine whether, in operation, satisfactory cold exchangewill take place between the air and the nitrogen and oxygen products ofrectification, so that when such unit is assembled with other like unitsto form an exchanger of any desired capacity, the resultant exchangerwill give the desired cold exchange.

Another object is to provide a tubular exchanger, none of the tubes ofwhich need be provided with expansion joints.

Still another object is to provide an exchanger of the type disclosed,for example, in the copending application, Serial No. 641,276, nowPatent No. 2,529,516, consisting of a multiplicity of tubular exchangerunits having exterior fins in which, however, the exterior fins of oneunit do not have to be in bonded or metal-to-metal contact with theexterior fins of adjacent units for satisfactory operation, therebygreatly decreasing the construction cost, and simplifying the assemblyof the multiplicity of units constituting the exchanger.

Other objects and advantages of this invention will be apparent from thefollowing detailed description thereof.

In the accompanying drawings forming a part of this specification andshowing for purposes of exemplification preferred forms of thisinvention without limiting the claimed invention to such illustrativeinstances:

Fig. 1 is a composite view of a cold exchanger embodying this invention,the lower half being a vertical section through the exchanger, and theupper half a front elevation;

Fig. 2 is a fragmentary vertical section through one exchanger unitdiagrammatically showing how the pair of concentric tubes constitutingthis unit. are secured to the header plates at each end of theexchanger;

Fig. 3 is a diagrammatic horizontal section through the cold exchangerof Fig. 1, taken on line 3-3 of Fig. 1;

Fig. 4 is a fragmentary (one-quarter view) horizontal section, on .agreatly enlarged scale, showing one preferred arrangementof finsdefining the longitudinal channels associated with the concentric tubesof one exchanger unit;

Fig. 5 is a fragmentary (one-quarter view) horizontal section, on thesame scale as Fig. 4, showing a modified form of exchanger unit;

Fig. 6 is a fragmentary (one-quarter) plan view of a disk-type fin whichmay be employed in a cold exchanger embodying this invention;

Fig. 7 is an enlarged section taken in a plane normal to the disk finand passing through line 1-1 of Fig. 6;

Fig. 8 is a fragmentary (one quarter) plan view of another form of finwhich may be employed-in acold exchanger embodying this invention;

Fig. 9 is an enlarged section taken in a plane normal to thefin andpassing through line @-9 of Fig. 8;

Fig. 10 is a horizontal section through still another form of exchangerunit embodying this invention, this unitemploying fins of the type showninFigs. 6 to 9 Fig. 11 is a vertical section through the exchanger unitof Fig. 10, taken through line i l-l l of Fig. 10; and

Fig. 12 is a composite view of a cold exchanger involving exchangerunits of the type shown in Fig. 5; thelower half is a vertical sectionthrough the exchanger and the upper half a front elevation.

Referring to the drawings, I5 indicates a cylindrical shell which may beof nickel steel containing approximately 8% nickel, or of other suitablemetal. The shell is preferably in the form of a cylinder or drum havingconcavo-ccnvex ends It provided with centrally disposed openings IT atthe opposite ends thereof. Intermediate the ends of the shell I5 are aseries of raised and depressed portions or corrugations is extendingcompletely around the shell l5 and forming an expansion joint. Thisexpansion joint accommodates differential expansion and contraction ofthe shell l5 and the cold exchanger tubes which, as more fully desc ibedhereinafter, preferably are made of a metal, such as copper, of highthermal, conductivity capacity and of different coefficient of expansionthan the metal of shell 25. As above indicated, the constructioninvolves a nickel steel shell l5 and copper tubes, in which case theexpansion joints l8 are employed; the shell, however, may be of copper,and in view of the increased efficiency of the exchanger units of thisinvention, both the tubes and shell may be of steel, in which case ashell devoid of expansion joints may be employed.

Since both ends of the shell iii are of the same construction, only oneend will be described in detail. A pair of header plates i9 and 213 aresuitably welded to the walls of the shell as at 2| to provide agas-tight seal at each end of the shell. A series of ports 22 are formedin the walls of shell l5 in the area between the header plates l9 and20, these ports being equally spaced about the periphery of shell l5 andcommunicate with a manifold 23 extending circumferentially about theshell 15 in the area between the header plates. Manifold 23communicateswith a port or opening 24.

A second series of openings 25 are formed in the wall of shell I5equally spaced about the circumferential surface of the shell just abovethe header plate 2% viewing the lower end of Fig. 1, this series ofopenings leading into a manifold 25 extending circumferentially aboutthe shell. A port 2? communicates with this manifold. It will be notedthat manifolds 23 and 26 are formed within a single manifold by means ofpartition 23a. Thus there are provided at each end of the shell, anoxygen header 28 communicating with the ports 22 which in turncommunicate with the manifold 23, a second header 29 communicating withport H, and a third header 30 which,- through ports 25, communicateswith the manifold 26 having port 21. The flows of air and nitrogenduring one cycle of operation, indicated by full line arrows in Fig. 1,take place through headers 38 and 29, respectively, and, upon reversalduring the subsequent cycle of operation, the flows of air anadnitrogen, as indicated by dotted line arrows, take place through theheaders 29 and 39, respectively. Oxygen flows continually through header28.

In accordance with this invention, each tubular unit disposed within theshell consists of three zones, namely, a first zone for flow of oxygentherethrough, a second zone for flow of nitrogen or air, and a thirdzone for fiow of air or nitrogen, fiow through the second and thirdzones being periodically reversed. The cold exchange surface associatedwith each unit is so proportioned and designed that the desired coldexchange takes place between the three streams flowing through eachunit, i. e., the air exits at the desired low temperature. Hence, eachunit is self-sufficient from the viewpoint of heat transfer and canbeseparately tested and evaluated before assembly in the shell. Byassembling a plurality ofsuch units, preferably with a smallclearancebetween contiguous units to facilitate the ready assemblythereof, the number thus assembled depending l upon the desiredcapacity, a cold exchanger results which is eminently satisfactory andefficient in operation.

In the embodiment of the invention shown in Figs. 1 to 4, zone I, theoxygen zone is theannular space 3| between an inner tube 32 anda.concentric outer tube 33, zone2 is disposed in the interior of tube32, and zone 3 is substantially that outlined by the foil-like metal fin34 .(Fig s 3 and 4) secured to the exteriorv of the tube 33 which fin inthe embodiment of the invention shown in Figs. 3 and 4 has a hexagonalexterior outline. The tubes 32 and 33 are made of electrolytic copperwhich is of a high heat transfer capacity, or other metals such asaluminum or alloys of high heat transfer capacity. The tubes arepreferably cylindrical; ho ever, a hexagonal tube or even a square tubey be used, if desired; hence, the term tube is used in a broad sense andis intended to include all such polygonal tubular members.

The tube 32 (Fig. 4) is provided with an interior fin 35 and an exteriorfin 36, the fins being of a metal of high thermal conductivity,preferably copper, and of foil-like thickness, for example, from .005"to .020" in thickness, preferably a thickness of .008" to .010 Fin 33,it will be noted, functions as an interior fin for tube 33, the lattertube having the exterior fin 34 hereinafter more fully described. Theinterior fin 35 is constructed and arranged to provide a multiplicity ofinterrupted contiguous channels extending longitudinally through tube32. In the preferred embodiment shown in Fig. 4 of the drawings, theinterior fin 35 for each section of tube length is produced by foldingfour strips of foil-like copper, one of which is shown in Fig. 4 infolded position, to form the triangular channels 31 having their basesin contact with the interior wall of tube 32 and their apices disposedremote from this wall, and other triangular channels 38, the apices ofwhich are disposed near the wall of tube 32 and the bases of which aredisposed along radii of the tube 32. Each strip of foil-like copperproduces triangular channels 31 and 38, completely filling one-fourth ofthe cross-sectional space of the tube 32, the bases of the triangularchannels 38 formed by the adjacent strips being in contact with eachother'and the four strips providing triangular longitudinally extendingchannels completely filling the cross-sectional space within the tube.The longitudinally extending channels are interrupted at spacedintervals by narrow slots like slots 39 (Fig. 1) as hereinafter morefully described.

The use of four strips folded accordion-like to form longitudinallyextending channels, triangular in cross-section, as hereinabovedescribed, results in the fin maintaining the position shown in Fig. 3.In other words, where the bases of triangles defining the channels arein contact with each other along the radii of the tube, the channelwalls are, in effect, reinforced so as to prevent collapse which mightotherwise take place in view of the extreme thinness of the fin. Asabove indicated, these fins are preferably of a thickness of from .008to .010". Collapse of the channel walls would be wasteful of heatexchanger surface. When tube 32 is comparatively small or fin 35 is madeof comparatively heavy foil, fin 35 may be made by folding accordionlikeonly two strips of copper so that the bases of the triangular channels38 of the two adjacent strips are in contact with each other along thediameter of tube 32.

Fin 36 disposed in the annular space between tubes 32 and 33 ispreferably formed by folding, for each section of tube length, a stripof foillike copper into the shape shown in Fig. 4 to provide alternateportions in contact with the inner wall of tube 33 and the outer wall oftube 32 connected by inclined portions, thereby forming two sets ofsubstantially triangular longitudinally extending channels 40 and 4|.Eachstrip of foillike copper so folded may be approximately two incheswide, and adjacent strips are preferably separated by a narrow slotsimilar to slot 39..

The fin 34 is folded to provide two sets of contiguous triangles 42 and43, the bases of the triangles 43 being in flat contact with theexterior of the tube 33 and the bases of the triangles 42 being remotefrom the wall of tube 33 and forming a hexagonal outline, as clearlyshown in Fig. 4. Instead of the hexagonal outline of Fig. 4, thetriangles may be arranged to produce a substantially square or otherpolygonal outline; the hexagonal outline is preferred. The exterior fin34 may be made from one piece of foil-like metal or a larger number ofpieces, for example, two pieces each of a length adequate to formonehalf the hexagonal outline, or even six pieces each of a length toform one side of the hexagonal outline.

The accordion-like fins on the interior of tube 32 and exterior of tube33 are formed by folding strips of foil-like copper 4" to 12" wide,preferably about 6" wide. The triangular channels provided by these finsections are, therefore, 4" to 12" long along the tube length, therebeing a multiplicity of these fin sections arranged serially along eachtube and separated by a space or slot like slot 39 shown in Fig. 1between adjacent fin sections 34 attached to the exterior of tube 33.These slots 39 are relatively narrow, say from T 5" to A," wide,preferably about I a" wide. Wider slots may be used but are wasteful ofexchanger metal and volume. Such spaces or slots are left betweenadjacent fin sections on the interior of each of the tubes 32 and 33, aswell as between adjacent fin sections attached to the exterior of tube33. Also, adjacent fin sections along the length on the interior of tube32 and, if desired, on the interior of tube 33, may be staggered, i. e.,may be positioned out of longitudinal alignment. With the constructionherein described, turbulent gas fiow takes place through the channelsformed by both the interior and the exterior fins on the tubes. In otherwords, the spaces or slots 39 occurring at intervals of every 4" to 12"in fins 34 and 35 and every 2" in the case of fin 3B, induce turbulencein the gas streams which would otherwise have a streamlined ortransitional flow. The distance between the slots is such that at aboutthe point where the turbulence induced by one slot disappears, there isanother slot to make the stream turbulent again. Furthermore, thestaggering of adjacent fin sections augments the turbulence induced bythe slots.

The fins 34, 35 and 36 are desirably bonded to their respective tubewalls with which they are associated by coating the interior andexterior surfaces of the tubes 32 and 33 with solder metal, placing thefin sections, folded as shown in Fig. 4 and spaced to provide the slotsbetween adjacent sections, in contact with the solder coating, thenplacing the assembly in an oven and heating it to a temperature so thatthe solder on the tube walls wets the fins and later cooling, therebyobtaining a firm bond between the tube walls and the portions of thefins in flat contact with the tube walls.

From Figs. 1 and 2 it will be noted tube 32 is of somewhat greaterlength than the concentric larger diameter tube 33, tube 32 being of alength to extend from one header plate l9 to the other header plate illat the opposite end of shell l5. The space between the end of tube 33and the end of tube 32 is substantially the same as the distance betweenthe two header plates I9 and 20, as is evidentfrom Fig. 1. Tube 33.. isof a. length to extend between. the two. header plates 20. The fins 34on the exterior of tubes. 33 do not extend to the ends of these tubes,but the portions of the tubesdisposed within the headers 33 are leftfree of fins, thereby forming the headers 35' at opposite ends of theshell in the area of the shell containing the ports 25.

The ends of tube 33, as shown in Fig. 2, are. secured to the headerplates 20, preferably by disposing the ends within openings 44' in theheader plates 2c andbrazing the tubes to the header plates as at 55. tomakea gas-tight joint with the header plates. The portions'dfi of theinner tubes 32 near the header plat-es 2b: are flared to: provide anannular space 41 of greater Width than that of space 3|. The largerannular space i! is desirable since more room is thereby provided forinserting tools or other means by which the end of tube 33 is attachedto plate 28 as by brazing at 25. This enlarged annular space M can alsobe obtained by flaring tube 33 outwardly instead of flaring tube 32inwardly as shown. Theends of tubes 32 are dis posed within openings 48in the header plates 19 and brazed thereto as at is to form a gas-tightjoint with the header, plates 29. It will be'noted that the tubes 32are'secured to the header plates Is at their ends only; and where theypass through the header plates 29 are not secured thereto.Hence'differential expansion and contraction, if any, between thesetubes and the shell is taken up by the expansion joint !8. Tubes 33 aresecured at their ends only to the header plate 2%. of this inventioneliminates the necessity for employing special tubes having expansionjoints.

Each exchanger unit consisting, tubes 32 and 33 having interior andexterior fins 3d, and 36, as hereinabove described, are assembled in abundle which, as shown in Figs. 1 and 3, is di posed within shell E5.The individual tubular units may have a small clearance between thebases of the triangular channels 22 associated with one unit and thebases of these channels associated with contiguous u..ts, therebygreatly facilitating the assembly of the units within the shell. Thespace between the exterior of the bundle of tubes and the interior ofthe shell is at intervals along the length of the shell is blanked-offby bafiie plates iii: (Fig. 1) which prevent flow through this space andinsure that-flow of gas through liltBirfididtB portion of shell it takesplace through the channels defined by the exterior fins on the tubes 23.These baflies 58 also act as reiniorcingstays aligning the tube bundlewithin the shell 55. The spaces between bafiles 56 may be filled withpacking 5i, e. g., crumpled aluminum foil or wood blocks. The shell, ifdesired, may be made closs-fitting relative to the tube bundle, therebyeliminating the bafiles and packing.

In the modification of Fi 5, the oxygen zone is disposed within tube 52and the air and nitrogen zones, which are periodically reversed ashereinabove described, disposed within tube 53 concentric with tube 52and the triangular channels formed by fin 54 on the exterior of tube 53.Tubes 52 and 53 are of any metal of high heat conductivity. Fins 54, and55, associated with these tubes, are of copper or other metal of highheat conductivity.

F111 53 disposed withintube 52 may be produced in. the same manner asfin 35 hereinabove described; and hence'need not be described inAccordingly, the construction 8 further detail. of tube. 53 may beformed in the same manner as fin 34 on the exterior of tube 33. Fin 55disposed in the annular space between tubes.52' and.

53 is constructed and arranged to provide a multiplicity of interruptedchannels extending longitudinally througfi the tube 53. This fin foreach section of tube length is produced by folding a strip of foil-likecopper or other metal to form two sets of substantially isoscelestriangles which completely n11 the space between, tubes 52 and 53. Oneset of triangles 51 have their base portions in flat contact with theinterior wall of the tube 53 and their apices contiguous to the exteriorwall of tube 52. The other set of triangles 58 have their bases in flatcontact with the exterior wall of tube 52 and their apices contiguous tothe interior wall of tube 53.

As in the case of the construction of Figs. 1, 2 and 3, thelongitudinally extending channels formed by the fins 5 3, 55 and 55 areseparated by narrow slots which may be approximately in width atintervals of from i" to 12', preferably about 6', adjacent sections offins and 56 alon the length of the interior of tubes and be staggered inorder to induce turbulence of the gaseous media flowing through thesesections. Als the fins are bonded to the of the tubes 52 and 53 in thesame manner as hereinabove described in connection with the bonding ofthe fins 36, 35 and to the walls of tubes 32 and 33, in the modificationof E l, 2 and he individual units of the modification of ereinab- 5Qdescribed, arranged with e units a shell to form exchanger of 5165-165.capacity o shown in Fig. 12 in which like those of 1 have been givenlike reference characters. In the construction of Fig. 12 there isprovided at each end of the shell, an oxygen header 2& communicatingwith the interior of tubes 52 and port El, a header 28 cornx: unicatingwith the interior of tubes 53 and through ports 22 is and a header 3communicating with the channels formed by fins 54 on the exterior oftubes 53 and through ports 25 with manifold 26 having port 2?. The flowsof air and nitrogen during one cycle of operation, indicated by fullline arrows in Fig. 12, take place through headers 3t and r spectively,and upon reversal ng the su. uent cycle of operation, the o s of air andas indicated by dotted place through the headers 28 arrows, take 38respectively. Oxygen flows-continually 1 ugh header 29 The modificationof Figs. 6 to 11 resembles that (iii constitutes the oxygen zone'and andnitrogen Zones are disposed'withintube and in the channels formed by thefins on the exterior of tube 5%, flow through the latter two zones beingperiodically reversed. In the modification of Figs. 6 to -ll, thechannels within tube formed by positioning within this tube insubstantially abutting relationship, a multiplicity of disks Si of thetype shown in Figs. 6 and 7. These disks may readily be produced bysimple stamping operation and with no waste of material from copper orother material of hi rh heat conducting propertiesof foil-likethiclrnes. say from .005 toqOZO inch; Each disk 65 an integral flange 62on the periphery thereof and has intheface thereof two seriestS and (iof radially-disposed closely- Likewise fin v54 on the. exterior withmanifold having port spaced passages 65 and 66. The two series ofpassages are separated by a flat portion 6'! of the disk ofsubstantially circular outline. The passages 65 are each formed bycutting the disk along pairs of radial lines 69 and 69 and thendeflecting or twisting the material between each pair of lines so as tomove this material out of the plane of the disk about points 19 aspivots and form vanes H. In like manner, the passages 66 are formed bymoving the material between each pair of radial cuts 12 and T3 to formthe bafiies 14. Thus there are produced baflles or vanes H and 14 actingas the walls of the two series of channels or openings 63 and 64,respectively, through which the gas flows. The disk 6| is preferablyprovided with a central hole 15 with a circular flange 16.

These disks are disposed within tube 59, as shown in Fig. 11, so thatthe flange 62 on one disk substantially abuts the face of a contiguousdisk within tube 59. Flow through the openings 65 and 66 of the diskswithin the tube 59 is guided by the vanes or bafiles H and. 14, which,in effect, form the longitudinally extending channels, radially disposedwithin this tube.

The fin 1'! within the annular space between the tubes 59 and 60 may beof the same construction and design as fin 36 between the tubes 32 and33 of the modification of Fig. 4 and may be formed in sections separatedby narrow slots 18 comparable to slots 39 in the modification of Fig. 4.

The fin 19 on the exterior of tube 60 in the modification of Figs. and11 is formed from a series of disks of the type shown in Figs. 8 and 9.These disks may be made of copper of coil-like thickness, say from .005"to .020" thick and produced by a simple stamping operation. Each diskhas an interior circular outline 86 adapted to conform to the shape ofthe tube 60 on which it is mounted, the interior edge 89 having integraltherewith a flange 8|. The opposite edge 82 of the disk is preferably ofpolygonal shape, e. g., a hexagonal shape as shown in Fig. 8. Edge 82 isprovided with an integral flange 83. The face of the disk is out alongclosely-spaced lines 84 and 85 and the material between these linesdeflected or rotated about points 86 and 81 as pivots to produce baffles88 which guide the gas through the openings 89 thus formed.

As shown in Fig. 11, these disks are assembled on the exterior tube 60so that the flange 8| of one disk substantially abuts the face of acontiguous disk; the openings 89 which in effect are a multiplicity oflongitudinally extending channels formed by baflies 88 are interruptedat closely-spaced intervals, i. e., between each pair of contiguousdisks.

The construction hereinabove described, it has been found, provides anexceptionally high area of heat exchanger surface per unit of volume ofexchanger and. thereby greatly increases the heat transfer rate. In thefins of the type shown in Figs. 6 to 9, the vanes or baffles arerepresented as being at right angles to the plane of the disks. However,the vanes may be set at an angle of from 60 to 90 with the plane of thedisk. For more complete disclosure of these disk-type fins, referencemay be had to copending application of Herman F. Buschow, Serial No.678,464 filed June 21, 1946, now Patent No. 2,532,288.

The individual exchanger units of Figs. 10 and 11 are arranged withother like units in a shell to form an exchanger of desired capacity,the shell being provided with oxygen, nitrogen and air headers similarto those of Fig. 1.

In the operation of the modification of Figs. 1 to 4, flow of oxygen, asshown by full line arrows, takes place through the port 24 into manifold23, ports 22, header 28, thence through all the oxygen tubes 33 of theassembly of units within the shell 15 into the header 28 at the oppositeend of the shell [5, the oxygen leaving through the ports 22, manifold23 and port 24 associated with the last-mentioned header 28. This flowis continuous throughout the operation of the exchanger, i. e., noreversal of the oxygen flow takes place. During one period of operation,nitrogen, as shown by the full line arrows, enters through port 11 andheader 29 at the same end of the shell at which oxygen enters, flowsthrough tubes 32 into the header 29 at the other end of the shell andexits through the top port l1. At the same time, air enters at the topport 21, flows through manifold 26, ports 25 and then through thechannels 42 and 43 formed by fins 34 and exits through the ports 25 intomanifold 26, and thence through base port 21. The air, therefore, flowscountercurrently to both the nitrogen and oxygen streams. Upon reversal,as indicated by the dotted line arrows, air flows through the port I!into the top header 29, then through the tubes 32, exiting through theheader 29 and base port I1. During this reversal period, nitrogen flowsthrough base port 27, manifold 26, ports 25, header 30, then through thechannels 42 and 43 formed by the exterior fins 34, and exits throughheader 30, ports 25, manifold 26 and top port 21. As in the previouscycle of the operation, air flows countercurrently to both the nitrogenand oxygen streams.

In the operation of the modification of Figs. 5 and 12, flow of oxygen,as shown by full line arrows, takes place through base port [1 into theheader 29 thence through all of the tubes 52 of the assembly of units inthe shell l5 into the top header 29 the oxygen leaving through top portl'i. This flow is continuous throughout the operation of the exchanger,i. e., no reversal of the oxygen flow takes place. During one period ofoperation nitrogen, as shown by the full line arrows on Fig. 12, entersthrough base port 24 into manifold 23, flows through ports 22 into theheader 28 into and through tubes 53 into the top header 28 and exitsthrough ports 22, manifold 23 and port 24 at the top end of the shell.At the same time, air enters through the top port 21, flows throughmanifold 26, ports 25 and then through the channels formed by fins 54and exits through base header 39*, ports 25, manifold 26 and the baseport 21. The air therefore flows countercurrently to both the nitrogenand oxygen streams. Upon reversal, as indicated by the dotted linearrows, air flows through top port 24 into the top header 28 thenthrough the tubes 53, exiting through the bottom header 28 and base port24. During this reversal period nitrogen flows through base port 21,bottom header 39 then through the channels formed by the exterior fins54 and exits through top header 39 manifold 26 and top port 27. As inthe previous cycle of operation, air flows countercurrently to both thenitrogen and oxygen streams.

It will be noted the individual tubular units of the exchanger are eachself-suflicient in that each unit is so designed that the oxygen andnitrogen streams flowing therethrough cool the air stream to the desiredtemperatures. Hence, each unit can be tested and evaluated to determinewhether, in operation, satisfactory cold exchange will take placebetween the air and the nitrogen and oxygen products of rectification,and when such unit, found to be satisfactory upon test, is assembledwith other like units to form an exchanger of any desired capacity, theresultant exchanger will invariably be found to be eminentlysatisfactory and efiicient in operation and to have the desired coldexchange capacity. Furthermore, since each unit is designedindependently of the others to give the desired cold exchange, it is notnecessary to bond the exterior fins of contiguous units but a smallclearance may be left between continguous units of the tube bundleWithin the shell, thereby greatly facilitating the introduction of theunits within the shell to form an exchanger of desired capacity and themaintenance and repair of the exchanger in operation should it benecessary to replace one or more units. The clearances betweencontiguous exchanger units should be kept small, say about 1%", so as toprevent a large proportion of gas from flowing through these clearancesrather than through channels 42 and 43 of exterior fins 34.

It is well to note that both the accordion-type and the disk-type finscan be used in an exchanger unit of this invention. For instance, in theunit of Fig. 4, the internal accordion fin 35 may be replaced by a stackof disk fins 6| shown in Figs. 6 and 19. Also, in the exchanger unit ofFig. 10, the internal disk fin 6| may be replaced by accordion fin 35shown in Fig. 4. In the unit of Fig. 5, any one, two or all threeaccordion-type fins may be replaced by fins of the disk type; it isobvious that where the annular space between the concentric tubes isappreciable, say over about /2, the annular fin may be made by stampingdisks of foil-like metal similar to the disk fins 6i and 19 of Figs. 6and 8, respectively. Such an annular or ring-shaped fin would beprovided with flanges along the two edges, one for bonding to theexternal wall of the inner tubeand the other for bonding to the internalwall of the outer tube. Where the inner tube is comparatively small, thedisk fin of the type shown in Fig. 6 may be made with a single series ofradially disposed openings.

The tubes and fins assembled to form the exchanger units of thisinvention may be bonded to each other by using tubes and/or fins whichhave been precoated with solder, heating the assembly to melt the solderand cooling after the liquid solder has established metal-to-metalcontact between the tubes and fins.

The manifolding shown in Fig. 1 for introducing and withdrawing gases toand from the cold exchanger may take any of several forms. Analternative form of means for effecting the introduction and withdrawalof gases is shown with the cold exchanger of the copending applicationSer. No. 641,276, now Patent No. 2,529,516.

The cold exchanger has been shown in Fig. 1 in a vertical position withthe products of. air rectification entering at the lower end thereof. Ifdesired, air could'instead be introduced at the lower end of theexchanger and the products of rectification introduced at the upper end.Furthermore, particularly in the case of large exchangers, it isadvisable to support the cold exchanger in a horizontal position. Thereis also advantage in making the ports and associated headers at thewarmer end of the exchanger larger than the corresponding parts at thecolder end to compensate the volume changes occurring in the gaseousfluids flowing therethrough. Also, in some operations, the exchanger maybe employed without reversal of fluid streams.

An important advantage of the tubular exchanger units of this inventionover the use of two sets of tubes arranged for the flow of cold from oneset to the other as disclosed in copending application Ser. No. 641,276,now Patent No. 2,529,516, is that every exchanger unit in a bundle ofany number of such units will function as efficiently as any other unitin the bundle. In the arrangement of copending application Ser. No.641,276, now Patent No. 2,529,516, the tubes along the periphery of thebundle do not exchange as much cold as tubes which are completelysurrounded by contiguous tubes. Furthermore, the problem of evenlydistributing the set of oxygen tubes in relation to the other set oftubes in the tube bundle of the exchanger of application Ser. No.641,276, now Patent No. 2,529,516, does not arise in the exchanger ofthis invention.

It will be noted the cold exchanger has an exceptionally high surfacearea of cold exchanger surface per unit of volume of exchanger space.With the design of fins herein described employing as the outer tubescircular tubes of from 1 /2 to 4 outside diameter, preferably about 2/2" outside diameter, having a wall thickness of .035 to .125",preferably about .065", the exchanger may have from 300 to 500 squarefeet of cold exchanger surface per cubic foot of exchanger volume. Thefiat surface contact between portions of the exterior and interior finson the walls of the tubes results in high fin efficiency. The turbulentflow, caused by the spaced slots in the longitudinally extendingchannels, further improves the cold transfer efficiency of theexchanger. The exchanger is, therefore, of exceptionally high coldtransfer efiiciency. This makes it possible to have the volumetric spacethrough which nitrogen on the one hand and air on the other flowsrelatively small, thereby minimizing reversal losses. Moreover, the flowthrough the interior of the tubes and in the channels defined by thefins on the exterior of the tubes takes place in a general longitudinaldirection; hence, minimum pressure drop of fluid flowing therethroughoccurs.

Furthermore, the expansion joint in the shell accommodates differentialexpansion and contraction when the tubes and the shell are made ofdifferent metals having different coefficients of expansion, since thetubes are fastened to header plates at their ends only and not to anyadditional header plates intermediate to these end plates. With thisconstruction, therefore, it is not necessary to employ tubes havingexpansion joints, with consequent saving in construction costs.

Since different embodiments of the invention can be made withoutdeparting from the scope of this invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A heat exchanger comprising a cylindrical shell, at least two spacedheader plates at each of the opposite ends of the shell defining afirst, second and third header at each end of the shell, said firstheaders being contiguous to the ends of the shell, the said secondheaders being disposed between the two spaced header plates at each endof the shell contiguous to said first headers, and the said thirdheaders being disposed contiguous to the said second headers, means forsupplying oxygen rectification product to one of said headers, means forsupplying nitrogen rectification product to another of said headers,means for supplying air to the other of said headers, and a plurality ofindividual heat exchange units disposed in said shell in spaced relationto each other, each unit comprising a pair of concentric tubes in spacedrelation, the inner tube of each pair communicably connecting the saidfirst headers at opposite ends of said shell, the annular space betweenthe two concentric tubes of each unit communicably connecting the saidsecond headers at opposite ends of said shell, each inner tube havingtherein a large mass of foil-like metal permeated by a multiplicity ofclosely spaced channels separated from each other by said foil-likemetal, the annular space between the two concentric tubes of each unitbeing filled with a large mass of foil-like metal permeated by amultiplicity of closely spaced channels separated from each other bysaid foil-like metal, and the outer tube of each unit having thereon alarge mass of foil-like metal permeated by a multiplicity of closelyspaced channels separated from each other by said foil-like metal, thelast-mentioned channels communicably connecting the said third headersat opposite ends of said shell, whereby each unit has fiowingtheretfi'ough in indirect heat exchange relation separate streams ofair, nitrogen and oxygen rectification products and is thereforeself-sufficient from the viewpoint of heat transfer between the air,oxygen and nitrogen, the masses of foil-like metal on all of the outertubes filling substantially the entire transverse cross-sectional areawhich surrounds said outer tubes and is within said shell.

2. A heat exchanger comprising a cylindrical shell, at least two spacedheader plates at each of the opposite ends of the shell defining afirst, second and third header at each end of the shell, said firstheaders being continguous to the ends of the shell, the said secondheaders being disposed between the two spaced header plates at each endof the shell contiguous to said first headers, and the said thirdheaders being disposed contiguous to the said second headers, means forsupplying oxygen rectification product to one of said headers, means forsupplying nitrogen rectification product to another of said headers,means for supplying air to the other of said headers, and a plurality ofindividual units disposed in said shell in spaced relation to eachother, each unit comprising a pair of concentric tubes in spacedrelation, the inner tube of each pair communicably connecting the saidfirst headers at opposite ends of said shell, the annular space betweenthe two concentric tubes of each unit communicably connecting the saidsecond headers at opposite ends of said shell, each inner tube of eachunit having therein an accordion fin formed by folding sections of thinmetal of high heat conductivity to produce a multiplicity of shortclosely spaced, longitudinally extending passages completely filling thecross sectional area of said inner tube, a plurality of such sectionsbeing employed for each unit length of the tube and contiguous sectionsbeing separated by a narrow space, the annular space between twoconcentric tubes of each unit having therein an accordion fin folded toform two sets of triangular shaped passages with the bases of one set incontact with the inner wall of the outer tube and the bases of the otherset in contact with the outer wall of the inner tube, the outer tube ofeach unit having thereon a third accordion fin folded to form two setsof triangular closely spaced channels with the bases of one set incontact with the outer wall of the tube and the bases of the other setdisposed to produce a polygonal outline surrounding said tube, saidclosely spaced channels communicably connecting said third headers atthe opposite ends of said shell, whereby each unit has flowingtherethrough in indirect heat exchange relation separate streams of air,nitrogen and oxygen rectification products and is thereforeself-sufiicient from the viewpoint of heat transfer between the air,oxygen and nitrogen.

3. A heat exchanger as defined in claim 2 in which each of the tubes ofeach unit is of copper and the fins are also of copper and have athickness of from .005" to .020".

4. A heat exchanger as defined in claim 1,

having at .each end of said shell a pair of mamfolds on the outside ofsaid shell, one of said manifolds of each pair communicating only withthe third header through a series of openings spaced about the peripheryof said shell, and the other of said manifolds of said paircommunicating only with the second header through a series of openingsspaced about the periphery of said shell.

5. A heater exchanger as defined in claim 2, having at each end of saidshell a pair of cylindrical manifolds surrounding said shell andconcentric therewith, one of said manifolds of each pair communicatingonly with the third header through a series of openings spaced about theperiphery of said shell, and the other of said manifolds of said paircommunicating only with the second header through a series of openingsspaced about the periphery of said shell.

6. A heat exchanger as defined in claim 2 in which the polygonal outlineof the third accordion fin is an equilateral hexagon.

'7. A heat exchanger comprising a cylindrical shell, two spaced headerplates at each of the opposite ends of the shell defining a first,second and third header at each end of the shell, said first headersbeing contiguous to the ends of the shell, the said second headers beingdisposed between the two spaced header plates at each end of the shellcontiguous to said first headers, and the said third headers beingdisposed contiguous to the said second headers, a plurality ofindividual heat exchange units disposed in said shell in spaced relationto each other, each unit comprising a pair of concentric tubes in spacedrelation, the inner tube of each pair communicably connecting the saidfirst headers at opposite ends of said shell, the annular space betweenthe two concentric tubes of each unit communicably connecting the saidsecond headers at opposite ends of said shell, and the space surroundingthe outer tube of each unit communicably connecting the said thirdheaders at opposite ends of said shell, whereby each unit has flowingthere through in indirect heat exchange relation three separate fiuidstreams and is therefore self-sufficient from the viewpoint of heattransfer between the three fiuid streams, a pair of manifoldssurrounding said shell at each end of said shell, one of said manifoldsof each pair communicating only with the third header through a seriesof openings spaced about the periphery of said shell and the other ofsaid manifolds of said pair communicating only with the second headerthrough a series of openings spaced about the periphery of said shell,means for supplying one fluid stream to one of said first headers, meansfor supplying two other fluid streams to the pair of manifolds at oneend of said shell, means for withdrawing the one fluid stream from theother of said first headers, and means for withdrawing the two otherfluid streams from the pair of manifolds at the other end of said shell.

8. A heat exchanger as defined in claim 7 in which the pair of manifoldsat each end of the shell has a common wall separating the manifolds ofsaid pair.

9. A heat exchanger comprising a cylindrical shell, at least two spacedheader plates at each of the opposite ends of the shell defining afirst, second and third header at each end of the shell, said firstheaders being contiguous to the ends of the shell, the said secondheaders being disposed between the two spaced header plates at each endof the shell contiguous to said first headers, and the said thirdheaders being disposed contiguous to the said second headers, aplurality of individual heat exchange units disposed in said shell inspaced relation to each other, each unit comprising a pair of concentrictubes in spaced relation, the inner tube of each pair communicablyconnecting the said first headers at opposite ends of said shell, theannular space between the two concentric tubes of each unit communicablyconnecting the said second headers at opposite ends of said shell, eachtube of each unit having therein a large mass of thin high heatconducting material, which mass of high heat conducting material ispermeated by a, multiplicity of closely spaced channels separated fromeach other by said thin high heat conducting material, the outer tube ofeach unit having thereon a large mass of thin high heat conductingmaterial, which mass of high heat conducting material is permeated by amultiplicity of closely spaced channels separated from each other bysaid thin high heat conducting material and communicably connecting thesaid third headers at opposite ends of said shell,

whereby each unit has flowing therethrough in indirect heat exchangerelation three separate fluid streams and is therefore self-sufficientfrom the viewpoint of heat transfer between the three fluid streams, apair of manifolds surrounding said shell at each end of said shell, oneof said manifolds of each pair communicating only with the third headerthrough a series of openings spaced about the periphery of said shelland the other of said manifolds of said pair communicating only with thesecond header through a series of openings spaced about the periphery ofsaid shell, means for supplying one fluid stream to one of said firstheaders, means for supplying two other fluid streams to the pair ofmanifolds at one end of said shell, means for withdrawing the one fluidstream from the other of said first headers, and means for withdrawingthe two other fluid streams from the pair of manifolds at the other endof said shell.

PERCIVAL C. KEITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 164,757 North June 22, 1875516,349 Hall Mar. 13, 1894 745,312 Baragwanath Dec. 1, 1903 1,854,619Mortensen Apr. 19, ,2

1,920,800 McCausland Aug. 1, 1 33 1,980,791 Duggan et a1 Nov. 13, 19342,059,992 Gould Nov. 3, 1936 2,075,511 De Baufre Mar. 30, 1937 2,336,879Mekler Dec. 14, 1943 2,439,208 Gloyer Apr. 6, 1948 2,460,859 TrumplerFeb. 8, 1949 FOREIGN PATENTS Number Country Date 371,608 Great BritainApr. 28, 1932 881,258 France Jan. 22, 1943 44,339 Switzerland May 30,1908

